Radiotelephones generally refer to communications terminals which provide a wireless communications link to one or more other communications terminals. Radiotelephones may be used in a variety of different applications, including cellular telephone, land-mobile (e.g., police and fire departments), and satellite communications systems.
Many radiotelephones, particularly handheld radiotelephones, employ retractable antennas which may be extended out of, and retracted back into, a radiotelephone housing. Conventionally, retractable antennas are electrically connected to a printed circuit board containing radio frequency circuitry located within a radiotelephone housing. A conventional radiotelephone antenna is typically interconnected with the radio frequency circuitry such that impedance of the antenna and the radio frequency circuitry are substantially matched. Conventionally, an antenna and radio frequency circuitry are matched at about 50 ohms (.OMEGA.) impedance.
Impedance matching for retractable antennas may be difficult because antenna impedance may be dependent on the position of an antenna with respect to both a radiotelephone housing and internal radio frequency circuitry. When a retractable antenna is moved between extended and retracted positions, at least two different impedance states, may be exhibited.
Accordingly, with retractable antennas, it is generally desirable to provide an impedance matching system with dual circuits that provide an acceptable impedance match between an antenna and the radio frequency circuitry, both when the antenna is retracted, and when the antenna is extended. Unfortunately, dual impedance matching circuitry can be somewhat complex and can increase the manufacturing costs of radiotelephones.
In addition, separate sets of signal line terminals or contacts are often used with impedance matching circuits to electrically connect a respective matching circuit to an antenna element. Unfortunately, multiple feed contacts may add to the complexity of the design and manufacturing of radiotelephones. Furthermore, multiple feed contacts may require multiple mechanical parts, such as spring contacts, that may become unreliable over time.
Many of the popular hand-held radiotelephones are undergoing miniaturization. Indeed, many of the contemporary models are only 11-12 centimeters in length. Unfortunately, as radiotelephones decrease in size, the amount of internal space therewithin may be reduced correspondingly. A reduced amount of internal space may make it difficult for retractable antennas to achieve the bandwidth and gain requirements necessary for radiotelephone operation because antenna size may be correspondingly reduced. Furthermore, radiotelephone antennas may not function adequately when in close proximity to a user during operation, or when a user is moving during operation of a device. Close proximity to objects or movement of a user during operation of a radiotelephone may result in degraded signal quality or fluctuations in signal strength, known as multipath fading.
It is also becoming desirable for a radiotelephone antenna to be able to resonate over multiple frequency bands. For example, the Japanese Personal Digital Cellular (PDC) system utilizes two "receive" frequency bands and two "transmit" frequency bands. Accordingly, radiotelephone antennas used in the Japanese PDC system should preferably be able to resonate in each of the two receive frequency bands. Unfortunately, the ability to provide retractable antennas with adequate gain over multiple frequency bands may be presently limited because of size limitations imposed by radiotelephone miniaturization.